VEGETABLE CROPS

Stewart's Disease
of Corn

Fact Sheet Page 727.10 Date 1-1979

COOPERATIVE
EXTENSION  NEW YORK STATE  CORNELL UNIVERSITY

by
Arden Sherf and Thomas Woods Dept. of Plant Pathology Cornell University

Stewart's disease of corn is common throughout the eastern
United States. It is a bacterial disease, caused by the bacterium Erwinia stewartii
(E. F. Sm.) Dye. Unlike many fungal diseases of corn, damp weather and heavy
dews are not necessary for a disease epidemic to occur. The disease on sweet corn
is referred to as Stewart's wilt because of the wilting of foliage often associated
with infection. In addition to wilting, plants may be stunted, and in severe cases
death may result. Wilting and stunting are caused by slimy masses of bacteria,
which grow in the vascular tissue of the foliage and disrupt the normal metabolism
of the leaves. Symptoms of the disease on sweet corn may appear at any stage in
the development of the plant. The most diagnostic symptom of the disease is the
presence on the leaves of yellow to brown stripes or streaks with wavy or irregular
margins. These streaks may be quite short or may extend the entire length of the
leaf. The symptoms of Stewart's wilt may sometimes be confused with those of fungus
leaf blights or with frost injury. On field corn the disease is referred to as
Stewart's leaf blight. Symptoms usually do not appear until after tasseling. At
this time the characteristic streaks may be seen on the leaves of infected plants.
Several lesions may coalesce, and large areas of leaf tissue die with a resultant
loss in yield of ears. Wilting and stunting of field corn are rarely associated
with Stewart's leaf blight. Premature death of large areas of leaf tissue also
renders the plants more susceptible to stalk rots.

Click on photo for Magnification

Life
Cycle

The bacteria overwinter in the bodies of
adult corn flea beetles, small, shiny black beetles, which jump much like fleas
when disturbed while feeding. These beetles overwinter in the soil and, upon
emergence in the spring, commence feeding on and contaminating corn seedlings.
Up to 20 percent of beetles emerging from hibernation may carry the disease causing
organisms. Uninfested beetles soon pick up the bacteria by feeding on infected
plants and then spread the bacteria to healthy plants nearby. These beetles remain
able to infect healthy plants for the rest of their lives. An entire field of
corn may become infected in a relatively short period of time. Some or all plants
die, and severe yield reductions result.

Although
a few other species of insects have been shown to be able to transmit E.stewartii from plant to plant, none is as important in spreading the bacteria
as the corn flea beetle. A series of very cold winters may reduce the population
of overwintering flea beetles and thus lead to a decrease in incidence of Stewart's
wilt the current crop year.

The bacteria may survive
in infected seed for several months. Infected seed may be important in introducing
the bacteria into an area previously free of the disease; however, only about
2 percent of the plants developing from a planting of infected kernels develop
symptoms of Stewart's wilt. The infected plants may be fed upon by corn flea beetles,
which pick up the bacteria and spread them from plant to plant.

Control
Measures

Two major control measures are useful
in reducing losses to Stewart's disease. The first consists of planting tolerant
varieties, which will grow and produce well in spite of the presence of the pathogen.
In general, later maturing varieties are more tolerant of the disease than earlier
maturing ones, although several early maturing varieties are available with good
tolerance to Stewart's wilt. Current sweet corn varieties with tolerance include:
Bellringer, Calumet, Capitan, Comet, Defender, Gold Crest, Gold Cup, Gusto, Merit,
Midway, NK 199, Pacer, Seneca Chief, Silver Queen, Sprite, Sweet Sue, Titan, Valley
Market, Vanguard, Wintergreen, and Yukon. The second major control measure is
the application of early insecticide sprays for controlling the overwintering
flea beetle population. In areas where Stewart's wilt is known to be a potentially
severe disease, insecticides should be applied when the corn first breaks ground
and should be continued for several applications thereafter until the stand is
well established. Consult your county Extension agent for a list of registered
insecticides and rates of application.